This invention relates to a novel process for synthesizing a zeolite of the L type using organic and inorganic cations.
A synthetic, crystalline, potassium-containing zeolite designated as zeolite L is known to exhibit good catalytic properties, particularly for hydrocarbon conversion, and advantageous sorbent properties as described, for example, by Barrer et al., Surface Science, 12, 341 (1968). The chemical composition of zeolite L is disclosed in U.S. Pat. No. 3,216,789 to be: EQU 0.9-1.3(Na,K).sub.2 O:Al.sub.2 O.sub.3 :5.2 to 6.9 SiO.sub.2 :xH.sub.2 O
where x is 0 to 9.
Zeolite L and zeolites having related structures belong to the "L" family of zeolites. This family is characterized by having a 12-ring hexagonal structure with pore dimensions of about 5.5 to 7.2 .ANG.. In addition to Zeolite L, there are also barium zeolites Ba-G or Ba-G,L described by Barrer et al. in J. Chem. Soc., 2296 (1964), J. Chem. Soc., 1254 (1972) and J. Chem. Soc., 934 (1974); Linde omega disclosed in U.S. Pat. No. 4,241,036; zeolite ZSM-4 disclosed in U.K. Pat. No. 1,117,568; and the mineral mazzite which occurs in nature (see Galli et al., Contrib. Mineral and Petrologie, 45, 99 (1974)). ZSM-10, described in U.S. Pat. No. 3,692,470, may also be classified in this "family" of zeolites, as may Zeolite UJ described in U.S. Pat. No. 3,298,780.
Structures have been proposed for Zeolite L (Barrer et al., Zeit. Krist., 128, 352 (1969)), Linde omega (Barrer et al., Chem. Comm., 659 (1969)) and mazzite (Galli, Crystal Str. Comm., 339 (1974)). Galli et al., Contrib. Min. and Petr., 45, 99 (1974) have compared the data for zeolite L, omega and mazzite. Meier et al., Atlas of Zeolite Structures (1978) propose that mazzite, ZSM-4 and omega are isostructural differing only in Si/Al ratios and cation contents. If all cation positions in L are filled by alkali monovalent cations L will have a minimum Si/Al ratio of 1.8 according to Baerlocher et al., Zeit. Krist., 136, 253 (1972).
Typical preparations of zeolite L are disclosed in U.S. Pat. No. 3,216,789; Breck, Zeolite Molecular Sieves, New York: J. Wiley, 283 (1974) and U.K. Pat. No. 1,202,511 (wherein the product is a dry gel). Other workers have prepared zeolite L from gels, mixed base systems and metakaolin. See, e.g., Barrer et al., J. Chem. Soc. Dalton, 1258 (1972); Barrer et al., J. Chem. Soc. Dalton, 934 (1974); and U.S. Pat. No. 3,867,512 to Young.
U.S. Pat. No. 3,947,482 to Albers et al. describes synthesis of open framework zeolites such as zeolite L and offretite by reaction of a silica source, alumina source, sodium hydroxide and/or potassium hydroxide in the presence of a seeding (nucleation) slurry prepared using an organic template agent, which consists of quaternary compounds R.sub.4 M.sup.+ A.sup.- where M is a Group 5A element such as N or P and R is C.sub.1 to C.sub.7 and A.sup.- is an anion, and various complex organic ring compounds. The zeolite synthesis mixture itself contains no template.
Aiello et al., J. Chem. Soc. Dalton, 1470 (1970) discloses reacting oxide mixtures to synthesize zeolites including zeolite L in the presence of a tetramethylammonium cation.
U.S. Pat. Nos. 3,306,922; 3,308,069; 3,832,449; 3,972,983; 4,247,416 and 4,338,089 disclose synthesis of zeolites in the presence of tetraalkylammonium cations having alkyl groups of 2 to 4 carbon atoms. There is no disclosure of synthesizing zeolite L.
The established methods of synthesis generally yield either poorly crystalline products or submicrocrystalline particles which are difficult to recover from the mother liquor crystallization media, or use excess levels of reactants which create major water pollution problems.